This invention relates to a robot path error correction system for facilitating the drive and control of the movable element of a machine tool or the hand of a robot, the acceleration and deceleration of which is controlled.
In a control system for controlling the axial movement of a machine tool or robot, the conventional practice generally is to effect acceleration and deceleration in such a manner that the control system will not be subjected to shock or vibration at the start of axial movement and at deceleration. One example of such an acceleration/deceleration control method is to exponentially accelerate or decelerate the supply rate of pulses generated to correspond to the axially traveled distance.
FIGS. 5(a), (b), (c) are views illustrating drive states for a case in which two different velocity commands are programmed in succession. Time is plotted along the horizontal axis and velocity along the vertical axis. FIG. 5(a) illustrates a commanded velocity F1 from time t.sub.1 to time t.sub.2 for movement from a coordinate point P1 to a commanded position P2, and a commanded velocity F2 from time t.sub.2 to time t.sub.3 for movement to a subsequent commanded point P3. In actuality, however, when effecting movement to the commanded position P3 via the commanded position P2, a delay 2T is involved, as shown in FIG. 5(b), where T is the time needed for acceleration and deceleration.
The reason for this delay time is to carry out velocity control in such a manner that the control system will not be subjected to shock or vibration when starting and stopping movement in a case where axial movement of a machine tool or robot is controlled.
A method utilized to reduce this delay time is to ignore positioning at the intermediate commanded position P2 and effect acceleration up to the next commanded velocity F2 without performing deceleration at time t.sub.2. As shown in FIG. 5(c), this entails performing a pulse distribution calculation along each axis corresponding to the commanded position P3 based on velocity command pulses for accelerating a feed rate up to the commanded velocity F2 at time t.sub.2, which is the start of deceleration, and gradually driving the movable element in the designated direction. In accordance with this method, the resulting delay time is T. Moreover, by changing the commanded velocity, the robot trajectory can be made to approach a desired path.
Codes indicating these control functions are referred to as G11 and G12 and are used in an automatic acceleration/deceleration function, interpolation function and the like, as well as in the drive and control of machine tools. However, since the size of an arc described by the trajectory of the movable element changes whenever the commanded velocity changes, a system that corrects a path error by such control codes requires the creation of a complicated program in order to reduce the path error of the robot.